Plug valves have been used, and continue to be used, in various industries. The plug valve is relatively simple in construction, and may be used to control the flow of fluid, both liquid and gas, through various parts of a system. Many conventional plug valves include a substantially cylindrical plug that is rotationally mounted within a valve body. The valve body includes inlet and outlet flow ports. The plug additionally includes a flow passage that may be selectively aligned with the valve body inlet and outlet ports, or positioned transverse to the valve body inlet and outlet ports. When the plug flow passages are aligned with the valve body inlet and outlet ports, the valve is open, and fluid flow through the valve is allowed. Conversely, when the plug flow passage is transverse to the valve body inlet and outlet ports, the valve is closed and fluid flow through the valve is prevented.
The plug may include a pocket into which a segment seal is installed. In many plug valves, this pocket is positioned on the plug such that the segment seal is pressure loaded against the valve body outlet port when the valve is closed. As a result, the segment seal may experience relatively large radial forces in the closed position. Thus, when the plug valve is subsequently moved to the open position, the plug and segment seal may experience relatively high frictional forces. These high frictional forces may result in the need to use a higher power valve actuator than might need to be otherwise used, which can result in increased valve and system costs. Moreover, the high frictional forces can damage the segment seal and/or plug.
Hence, there is a need for a plug valve that experiences lower frictional forces, as compared to presently known plug valves, when it is being moved from a closed position to an open position, and/or a plug valve that does not rely on relatively high power actuators, and/or reduces the likelihood of segment seal damage during operation, and/or reduces valve and system costs. The present invention addresses one or more of these needs.